Railfan Technology > 110VAC to 74VDC transformer for Mars Light/Gyralite

I hope to buy a Mars light or Gyralite someday but understand that they run on 74VDC.  Is there a reasonably priced transformer I can buy to convert 110VAC to 74VDC?

Thanks!

I have a 74VDC Mars light and would like to know the answer also.

The Mars lite runs on Direct Current. Transformers only work on Alternating Current.

Sounds like you need some form of DC power supply that will take in 120 AC and send out 74VDC.

There might just be such a thing commercially available. Could be expensive depending on the current draw and how pure the DC needs to be. Some devices can tolerate a lot of ripple while others cannot..

Although in Canada try this:http://www.hammondmfg.com/product.htm

Bryce Lee
Burlington, Ontario

Any info on amperage? That would determine power supply requirements and cost. What the OP needs is someone who has already done this.

TCnR,

You are correct.  I am hoping that someone on TO already has a working Mars light or Gyralite running in their home and has already figured out how to reasonably power it.  I often see these for sale with the seller claiming they operate but what's the point if there isn't a good way to make it work at home?

Thank you everyone for your comments!

I don't have a Mars or Gyralight, but for my work I often need to power 74V equipment that goes on locomotives.    Because this is such an uncommon voltage it can be hard to find something inexpensive to fill the need.    
It is important to know how much current (amperage) you will need as well as the voltage.     A good guess is that you should have something that provides 10 amps or so.       Keep in mind that most locomotive equipment will operate on voltage anywhere from 60 to 80 volts, so you don't need something at exactly 74 volts.     Your light will probably be brighter and rotate faster at 75V than at 65V.   
Knowing what you need you can watch eBay for a DC power supply that meets your requirements.     If you are handy with electronics, or know someone that is, you can look for a step-down transformer that will provide an output near 70 volts AC and then connect that to a bridge rectifier to get DC.
Stephen



Edited 1 time(s). Last edit at 06/03/15 08:44 by rfdatalink.

It's a fairly simple electronics project to get 74 vdc, but you'll let the smoke out pretty quick trying to turn a rusty old 10 amp motor (suspect it will need even more than that).

Now knowing that I want a DC power supply is the answer.  I searched for variable DC power supplies and found a 0-120VDC 3A for $266 and a 0-100VDC 14A for $395.  So my next question is: How many amps do these lights need?

Trainweb has some good info.  It looks like they need up to 6 amps.  A post also has a way to drive them with AC.

You're going to need a ton of current to run this thing at its rated power.  Locomotive headlights draw between 5-7A each (be it a 200W 30V or a 350W 74V) and have significantly higher inrush until they warm up.  (Any idea what bulbs are in yours?) 

The motor current will probably be the least of your worries.  By what I understand, it's <0.5A at 74V.

I would look at powering it by getting two 36V, 350W switching power supplies off Amazon or eBay (Meanwell is a well known vendor that makes quality units, but there's a zillion clones of various trustworthyness), wire them in series to give you 72V, and then power it from that.  Just don't forget to use adequately heavy wire and adequately rated switches, and a fuse in the input side of each wouldn't hurt either.
 

Thanks!  As I said in my OP I don't have a light but want to know how to make them operate when I do get one.

I did a bit of searching to see what the current requirements were for a Gyralite and it seems I could find their exact dimensions, light output in candle power, and the type of bulbs they used, etc... but I didn't find anything about current.  I noticed that some used 30V and 32V bulbs, possibly is series, I don't know.  A 200 watt bulb at 30 Volts would be 6.25 Amps.  Put two in series, it would still take 6.25 Amps., just requiring twice the voltage, 60 or 64 Volts.  I could not find anything on current required to operate the motor in the units nor could I find any HP ratings.  I wouldn't suspect it would be a very large motor.  Theoretically, a 1 HP motor requires about 750 Watts but in practice you need a bit more to overcome friction and heat losses.  At 74 Volts, a 1 HP motor would require a little over 10 Amps.  I suspect the motor would be quite a bit smaller than that since it's only moving a light bulb and a reflector,  It's not cutting your grass or turning a fan or spinning your clothes in a sewing machine.  It's probably overpowered / overbuilt but not more than a quarter  or tenth HP.  I could be wrong but that would be a guess.

So, you are going to need 6 or 7 Amps just to light the lamps (I guess that would make a nice night light in your hall) and probably 4 or 5 more Amps to turn the motor, or a total of 10 to 12 Amps.  THIS IS ONLY A GUESS.  Don't go out and make a purchase based on my guesses.  This also assumes that the motor and gears are clean, lubricated, and in general, in good shape.  If you were building a power supply you would not need a 75Volt output on your transformer.  A sign wave from a transformer with 50 VAC output has that reaches 70.7 Volts peak (50 X 1.414,) and when filtered to a reasonably smooth DC would probably end up around  60 or65 VDC.  A transformer power supply would be the simplest.  It would also weigh about the same as a small anvil.  Newer power supplies are being built without transformers.   They are much lighter, have electronic regulations and a smoother output in many cases.  They are more complicated to build if you don't dabble in electronics.  I have no idea of what they would cost you but Lambda and Magna-power are two manufacturers of such supplies.  There are many others.  Search "transformerless power supply" to find some.

I wish I could help you more but that's all I can come up with at this time.  I don't even want to look at the prices on the supplies.  You would need about 750 to 1000 Watts.  I decided to look into this since no one else had come up with any answers.  Now I sort of know why.  The information is out there somewhere but I just don't know where and I didn't want to spend hours looking into it.  I did search for about an hour.

You're just going to have to find someone with one working to find out what the power requirements are or someone that has, or has access to the documentation on the lights.

Good luck,

John
 

John immediately above is close on!
A locomotive headlight is 300 Watts at 30 Volts DC, so add 50% to his lamp amps for two lights in series, and the motor is less than 1/4 hp, so you can figure it all out.
The SP's Mars/Gyralites ran the two bulbs in series, so when one failed, you lost the whole light.  Headlights have two separate resistor circuits, so only one bulb goes out at a time.
30 Volts is a full bright headlight, I don't remember what voltage medium and dim are, something like 25 and 20 Volts.

Ditch light bulbs are 74 Volt.

To determine DC voltage from a transformer output, divide the output by 0.707, or multiply it by 1.414.
G

Thanks everyone again for the info!  Looking at the trainweb posts one recommended that for indoor use to only have a fraction of the voltage for the lamps because you don't need a blinding light.  That would greatly reduce the required amps.  They also suggested putting the lamps and motor on separate circuits.

meixel Wrote:
-------------------------------------------------------
> Thanks everyone again for the info!  Looking at
> the trainweb posts one recommended that for indoor
> use to only have a fraction of the voltage for the
> lamps because you don't need a blinding light.

That sounds like a great idea.  I don't know how you were going to use the light but I was wondering if you were going to use welders goggles to look at it.  A bit of overkill for a nightlight in the hall.  On the other hand, you could light the entire back yard and just tell your friend you live at the house with the bright light in the back yard, you can't miss it.  You could use some sort of 12 Volt supply for the lights.  It wouldn't even have to be DC.  Light bulbs don't care whether it's AC or DC.  A slight rewire to put the bulbs in parallel shouldn't be a big problems.  You could also put a power resister in series with the lamps to dim them further if you wanted to.  The bulbs are 30 or 32 Volt bulbs and 12 Volts might be close enough to make you happy.  You could even use an old car battery with a trickle charger if you didn't intend to use it all the time.  Of course, that not look to nice in the living room.  Kind of hard to figure how much current you would need in that situation.  A 200 Watt, 30 Volt would require 6.67 Amps but the resistance of the filaments changes as they heat up.  12 Volts would force less current through the filament but not sure how to figure out how much since the resistance does change

>  That would greatly reduce the required amps.  

A 74 Volt supply at an Amp or two would sure be a lot easier to handle and it would save you a lot of money.  I really don't have even a ballpark figure on what the motor would require.  I suspect less than 2 Amps but I just don't know.  Two Amps would be about 150 Watts and that would produce a tenth of a horsepower.  A typical 18" oscillating fan has about 1/20th HP motor.

>  They also suggested putting the lamps and motor
> on separate circuits.

John

Thanks!  Yes I think my homeowners association might have a problem with a bright outdoor Mars light!  It might be a cool burglar alarm!?



Edited 1 time(s). Last edit at 06/07/15 05:13 by meixel.

I have built two power supplies for my railcars that supply power for a anti-wheel slide system, Wabco E-5. They require 62-78 volts DC that run the system.  I start out with 120 Volts AC feeding a Acme TB54523 transformer.  The output voltage is 50 Volts AC RMS. That is right 50 V The 50 Volts is put through a full wave bridge that can be purchased at an electronics store, at low cost, and a 1548 MFD capacitor. These are used as motor starting cap. These can be purchased at an electrial supply, also at low cost,  rated at 250 Volts min.  End result is 64 Volts DC that has lows ripple. 

Alvin Bishop
Costa Mesa, CA
California Zephyr Railcar Charters

The Mars lights and Pyle(?) Gyralights were also found on fire trucks to make these vehicles more visible. There may be ways to convert the railroad lights to 12 vdc service.

Posted from Windows Phone OS 7